Shedding light on baryonic dark matter

Halo dark matter, if it is baryonic, may plausibly consist of compact stellar remnants. Jeans mass clouds containing 10(6) to 10(8) solar masses could have efficiently formed stars in the early universe and could plausibly have generated, for a suitably top-heavy stellar initial mass function, a high abundance of neutron stars as well as a small admixture of long-lived low mass stars. Within the resulting clusters of dark remnants, which eventually are tidally disrupted when halos eventually form, captures of neutron stars by non-degenerate stars resulted in formation of close binaries. These evolve to produce, by the present epoch, an observable x-ray signal associated with dark matter aggregations in galaxy halos and galaxy cluster cores.     

Missing mass in collisional debris from galaxies

Recycled dwarf galaxies can form in the collisional debris of massive galaxies. Theoretical models predict that, contrary to classical galaxies, these recycled galaxies should be free of nonbaryonic dark matter. By analyzing the observed gas kinematics of such recycled galaxies with the help of a numerical model, we demonstrate that they do contain a massive dark component amounting to about twice the visible matter. Staying within the standard cosmological framework, this result most likely indicates the presence of large amounts of unseen, presumably cold, molecular gas. This additional mass should be present in the disks of their progenitor spiral galaxies, accounting for a substantial part of the so-called missing baryons.     

Direct detection of galactic halo dark matter

The Milky Way galaxy contains a large, spherical component which is believed to harbor a substantial amount of unseen matter. Recent observations indirectly suggest that as much as half of this "dark matter" may be in the form of old, very cool white dwarfs, the remnants of an ancient population of stars as old as the galaxy itself. We conducted a survey to find faint, cool white dwarfs with large space velocities, indicative of their membership in the galaxy's spherical halo component. The survey reveals a substantial, directly observed population of old white dwarfs, too faint to be seen in previous surveys. This newly discovered population accounts for at least 2 percent of the halo dark matter. It provides a natural explanation for the indirect observations, and represents a direct detection of galactic halo dark matter.     

The dark halo of the milky Way

Most of the matter in the Milky Way is invisible to astronomers. Precise numbers are elusive, but it appears that the dark component is 20 times as massive as the visible disk of stars and gas. This dark matter is distributed in space differently than the stars, forming a vast, diffuse halo, more spherical than disklike, which occupies more than 1000 times the volume of the disk of stars. The composition of this dark halo is unknown, but it may comprise a mixture of ancient, degenerate dwarf stars and exotic, hypothetical elementary particles.     

Lighting the universe with filaments

The first stars in the universe form when chemically pristine gas heats as it falls into dark-matter potential wells, cools radiatively because of the formation of molecular hydrogen, and becomes self-gravitating. Using supercomputer simulations, we demonstrated that the stars' properties depend critically on the currently unknown nature of the dark matter. If the dark-matter particles have intrinsic velocities that wipe out small-scale structure, then the first stars form in filaments with lengths on the order of the free-streaming scale, which can be approximately 10(20) meters (approximately 3 kiloparsecs, corresponding to a baryonic mass of approximately 10(7) solar masses) for realistic "warm dark matter" candidates. Fragmentation of the filaments forms stars with a range of masses, which may explain the observed peculiar element abundance pattern of extremely metal-poor stars, whereas coalescence of fragments and stars during the filament's ultimate collapse may seed the supermassive black holes that lurk in the centers of most massive galaxies.     

The cosmic web in our own backyard

On the largest scales, matter is strung out on an intricate pattern known as the cosmic web. The tendrils of this web should reach right into our own cosmic backyard, lacing the Galactic halo with lumps of dark matter. The search for these lumps, lit up by stars that formed within them, is a major astronomical endeavor, although it has failed to find the huge expected population. Is this a dark matter crisis, or does it provide clues to the complexities of gas physics in the early universe? New technologies in the coming decade will reveal the answer.     

Giant ringlike radio structures around galaxy cluster Abell 3376

In the current paradigm of cold dark matter cosmology, large-scale structures are assembling through hierarchical clustering of matter. In this process, an important role is played by megaparsec (Mpc)-scale cosmic shock waves, arising in gravity-driven supersonic flows of intergalactic matter onto dark matter-dominated collapsing structures such as pancakes, filaments, and clusters of galaxies. Here, we report Very Large Array telescope observations of giant ( approximately 2 Mpc by 1.6 Mpc), ring-shaped nonthermal radio-emitting structures, found at the outskirts of the rich cluster of galaxies Abell 3376. These structures may trace the elusive shock waves of cosmological large-scale matter flows, which are energetic enough to power them. These radio sources may also be the acceleration sites where magnetic shocks are possibly boosting cosmic-ray particles with energies of up to 10(18) to 10(19) electron volts.     

温度和光照对商洛黄芩种子萌发的影响

为探讨商洛黄芩种子萌发的最适温度和光照条件,研究不同光照(全黑暗、10h光照+14h黑暗)和不同温度(15、20、25、30、35℃)条件下商洛黄芩种子萌发特性。通过对发芽率、发芽势、芽长、根长、鲜质量和干质量等相关指标测定得出,随着温度的升高,除芽长表现出逐渐上升趋势外,其他指标均呈先升后降趋势,发芽率、发芽势、干质量和根长都在20℃时达到峰值,芽长和鲜质量分别在30℃和25℃时出现峰值;除芽长在各温度下全黑暗处理均大于光暗结合处理外,在大于20℃条件下,各指标都表现为光暗结合处理优于全黑暗处理。结果表明,10h光照结合14h黑暗、20℃为商洛黄芩种子萌发的最适光照和温度条件,对于光暗结合处理抑制商洛黄芩芽长的原因还有待进一步探讨。     

Particle dark matter in the universe: at the brink of discovery?

The nature of dark matter is one of the central problems of cosmology, particle physics, and gravity. It may be made of still unknown particles produced in the early universe. Much progress has been made in attempts to detect these particles and in the development of the required experimental techniques. Results from direct searches, the Large Hadron Collider, and the Gamma-ray Large Area Space Telescope offer promising opportunities within the next decade to find the missing dark matter.     

Polarization observations with the Cosmic Background Imager

Polarization observations of the cosmic microwave background with the Cosmic Background Imager from September 2002 to May 2004 provide a significant detection of the E-mode polarization and reveal an angular power spectrum of polarized emission showing peaks and valleys that are shifted in phase by half a cycle relative to those of the total intensity spectrum. This key agreement between the phase of the observed polarization spectrum and that predicted on the basis of the total intensity spectrum provides support for the standard model of cosmology, in which dark matter and dark energy are the dominant constituents, the geometry is close to flat, and primordial density fluctuations are predominantly adiabatic with a matter power spectrum commensurate with inflationary cosmological models.     

黑垆土典型剖面养分分布特征及历史演变

利用土壤普查历史资料,采用原位采样及相同测定方法研究了不同时期典型黑垆土剖面的养分分布特征及演变趋势。结果表明:黑垆土剖面中有机质和全氮含量呈"S型"分布,均随土壤深度增加而呈下降趋势;全磷含量为"中低型"分布;全钾含量在整个剖面中基本趋于一致。与20世纪80年代相比,2008年黑垆土耕层有机质、全氮和全磷含量呈增加趋势,但在其他土层它们的含量均有不同程度的减少;全钾含量在整个土壤剖面均呈减少态势;耕层C/N平均值有所提高。     

New light on dark matter

Dark matter, proposed decades ago as a speculative component of the universe, is now known to be the vital ingredient in the cosmos: six times more abundant than ordinary matter, one-quarter of the total energy density, and the component that has controlled the growth of structure in the universe. Its nature remains a mystery, but assuming that it is composed of weakly interacting subatomic particles, is consistent with large-scale cosmic structure. However, recent analyses of structure on galactic and subgalactic scales have suggested discrepancies and stimulated numerous alternative proposals. We discuss how studies of the density, demography, history, and environment of smaller-scale structures may distinguish among these possibilities and shed new light on the nature of dark matter.     

花曲柳适生立地条件调查研究

通过对花曲柳天然分布，生长及其适生立地条件进行调查研究，发现花曲柳的适生立地条件为阳坡，半阳坡，半阴坡的山腹缓坡山谷，沟旁；土壤以间棕壤为主，土层以中厚层为宜，土壤结构为团粒状，粒状结构，通气良好，有机质含量高，土壤为微酸性。     

Why is the temperature of the universe 2.726 Kelvin?

The Cosmic Background Explorer satellite has recently made the most accurate measurement of the temperature of the universe, determining it to be 2.726 +/- 0.01 kelvin. In trying to understand why the temperature has this value, one is led to discover the most fundamental features of the universe-an early, radiation-dominated epoch, enormous entropy per nucleon, synthesis of the light elements around 3 minutes after the bang, and a small excess of matter over antimatter-as well as some of the most pressing issues in cosmology today-the development of structure in the universe and the identification of the nature of the ubiquitous dark matter.     

Testing cosmogonic models with gravitational lensing

Gravitational lensing provides a strict test of cosmogonic models because it is directly sensitive to mass inhomogeneities. Detailed numerical propagation of light rays through a universe that has a distribution of inhomogeneities derived from the standard CDM (cold dark matter) scenario, with the aid of massive, fully nonlinear computer simulations, was used to test the model. It predicts that more widely split quasar images should have been seen than were actually found. These and other inconsistencies rule out the Cosmic Background Explorer (COBE)-normalized CDM model with density parameter Omega = 1 and the Hubble constant (H(o)) = 50 kilometers second(-1) megaparsec(-1); but variants of this model might be constructed, which could pass the stringent tests provided by strong gravitational lensing.     

秦岭火地塘林区不同土壤类型腐殖质组成及结合态腐殖质特性的研究

对秦岭火地塘林区棕壤、暗棕壤及草甸土进行了分析测定。结果表明,不同土类在腐殖质组成及结合态腐殖质特性方面存在明显差异。棕壤、暗棕壤及草甸土的Ｈ／Ｆ值相比较,以暗棕壤最大,草甸土次之,棕壤最小;随剖面加深３种土类的Ｈ／Ｆ值明显下降。除草甸土、暗棕壤Ａ层外３种土类腐殖质均以富里酸为主。３种土类的结合态腐殖质均以松结合态为主,且以草甸土相对含量最高,暗棕壤次之,棕壤最低;随剖面加深,棕壤、暗棕壤及草甸土结合态腐殖质相对含量有增大趋势。３种土类的土壤有机质绝大部分是以结合态形式存在。     

柑橘、龙眼园土壤有机质与有效性养分质量分数的相关性

对福建省 781个柑橘园和 315个龙眼园的土壤进行分析 .结果表明 ,这 2种果园多数的土壤有机质质量分数处于良好水平 ;土壤有机质质量分数与有效性养分质量分数关系密切 ;土壤有效性养分质量分数随有机质质量分数的增加而增加 ;柑橘园与龙眼园土壤的有机质质量分数分别为 15- 35和 10 - 30 g· kg-1,其土壤有效性养分质量分数较为适宜 .因此 ,上述 2种果园的土壤有机质质量分数可作为较为适宜范围 .     

有机无机肥料配合施用对草甸暗棕壤有机质含量及作物产量的影响

经过20年长期定位试验,研究施用不同种类肥料对草甸暗棕壤有机质含量及作物产量的影响。结果表明:长期不施肥使土壤有机质含量持续下降;长期单施NP化肥能有效缓解有机质含量下降的趋势;长期单施有机肥以及有机、无机肥料配合施用能有效地提高土壤有机质的含量。尤其是有机、无机肥料配合施用不仅能有效提高土壤有机质的含量,并且在产量上较无肥及单施肥料的处理有明显的增产效果。     

鄂伦春旗耕地土壤有机质含量的时空变化趋势及其与大豆产量的关系

为全面分析鄂伦春旗土壤有机质含量随着时间推移发生的变化及在空间上的分布情况,比较该区域不同土壤类型有机质含量的差异,探讨土壤有机质和全氮含量之间的关系,对2008-2014年在鄂伦春旗域内均匀采集的7722个耕地土壤样品进行土壤类型判别及有机质、全氮含量测定,并与1986年全国第二次土壤普查数据进行对比,同时通过盆栽试...